From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Sasha Levin <sashal@kernel.org>
Cc: Thomas Lindroth <thomas.lindroth@gmail.com>,
kvm@vger.kernel.org, stable@vger.kernel.org
Subject: Re: Regression in v4.14.94 by "x86,kvm: move qemu/guest FPU switching out to vcpu_run"
Date: Mon, 28 Jan 2019 12:20:10 -0800 [thread overview]
Message-ID: <20190128202010.GA21909@linux.intel.com> (raw)
In-Reply-To: <20190128201453.GM3973@sasha-vm>
On Mon, Jan 28, 2019 at 03:14:53PM -0500, Sasha Levin wrote:
> On Mon, Jan 28, 2019 at 08:25:20PM +0100, Thomas Lindroth wrote:
> >I run a qemu/kvm VM with debian and I've started getting segfaults and failing checksums on
> >downloaded files. The failures are undeterministic and similar to the failures you get with
> >bad ram. I tried to diagnose the problem with various testing tools and found that
> >"stress-ng --verify --cpu 1" always give an error. Stress-ng give one of these errors
> >usually within 60 sec:
> >
> > stress-ng-cpu: Newton-Rapshon sqrt not accurate enough
> > stress-ng-cpu: prime error detected, number of primes between 0 and 1000000 miscalculated
> >
> >Nothing relevant has changed recently in the VM but the host kernel was upgraded from
> >4.14.93 to 4.14.96. I can't reproduce the stress-ng error with a 4.14.93 host kernel. There
> >is only one kvm related change in that range so I tried to revert that one.
> >
> >By reverting commit 4124a4cff344abbf8187775eb643d9827830e715
> >"x86,kvm: move qemu/guest FPU switching out to vcpu_run" on kernel 4.14.96 I can't reproduce
> >the stress-ng error and I have no segfault or other problems with the guest.
[...]
> Interesting, thank you for the report.
>
> Could you confirm whether this issue reproduces on a newer kernel that
> has that patch (4.19.18 for example)?
The bug is specific to 4.14, two dependent commits were applied in the
wrong order and introduced the bug. I have a patch, in the process of
typing up the changelog.
prev parent reply other threads:[~2019-01-28 20:20 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-28 19:25 Regression in v4.14.94 by "x86,kvm: move qemu/guest FPU switching out to vcpu_run" Thomas Lindroth
2019-01-28 19:53 ` Sean Christopherson
2019-01-28 20:14 ` Sasha Levin
2019-01-28 20:14 ` Sasha Levin
2019-01-28 20:20 ` Sean Christopherson [this message]
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